Metal fluorides as polycondensation catalysts



United States Patent 3,506,619 METAL FLUORIDES AS POLYCONDENSATION CATALYSTS Mary J. Stewart, Riddlewood, Media, and John A. Price,

Swartllmore, Pa., assignors to FMC Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Jan. 20, 1967, Ser. No. 610,489

Int. Cl. C08g 17/015 US. Cl. 260-75 Claims ABSTRACT OF THE DISCLOSURE Process of preparing polyethylene terephthalate comprising carrying out an ester-interchange reaction between ethylene glycol and dimethyl terephthalate or carrying out a direct esterification reaction between ethylene glycol and terephthalic acid and polycondensing the reaction product thereof in the presence of a metal salt of hydrofluoric acid.

This invention relates to an improved method for the preparation of linear polyesters. More particularly, it relates to an improved polycondensation catalyst for use in the manufacture of highly polymeric linear polyesters.

It is known that linear polyesters can be prepared from a suitable ester of a dicarboxylic acid or a dicarboxylic acid by initially reacting such a material with a diol. When an ester of a dicarboxylic acid is used as a starting ma terial, it is first reacted with a diol in the presence of a. transesterification catalyst by means of an ester-interchange reaction; Whereas, when a dicarboxylic acid is used as a starting material, it is first subjected to a direct esterification reaction with a diol in the presence of what is generally called a first stage catalytic additive or ether inhibitor. In either instance, the resulting reaction product which may be, in general, described as a polyester prepolymer, is then polycondensed in the presence of a polycondensation catalyst to form a polyester resin.

In the case of the transesterification method of preparing polyethylene wherein ethylene glycol is reacted with dimetryl terephthalate, the first stage product of the transesterification reaction is generally described as being comprised mainly of bis-2-hydroxyethyl terephthalate. Whereas, the first stage reaction product of the direct esterification reaction between ethylene glycol and terephthalic acid is comprised of bis-Z-hydroxyethyl terephthalate along with substantial quantities of higher condensates of ethylene glycol and terephthalic acid. In particular, the product of the direct esterification reaction between ethylene glycol and terephthalic acid and the product of the transesterification reaction between dimethyl terephthalate and ethylene glycol can be described as bis-Z-hydroyethyl terephthalate or a polycondensation product thereof, wherein the DP. (degree of polymerization) varies from about 2 to about 6. However, for purposes of simplicity in describing the present invention, hereinafter the terms polyester prepolymer and bis-2- hydroxyethyl terephthalate will both denote and include within their scope the product of the direct esterification reaction between terephthalic acid and ethylene glycol and the product of the transesterification reaction between dimethyl terephthalate and ethylene glycol as set forth above.

Heretofore, various materials have been suggsted as polycondensation catalysts for polycondensing the polyester'prepolymer products of both the transesterification method and direct esterification method of preparing polyester resins. However, in general, none of the substances that have been suggested as polycondensation catalysts heretofore have been completely satisfactory. For example, many of the polycondensation catalysts of the Patented Apr. 14, 1970 prior art only catalyze the condensation reaction to a low degree and they do not promote the reaction rate sufficiently to be acceptable for commercial purposes. Therefore, such polycondensation catalysts of the prior art do not act to form polyester products having carboxyl contents as low as required for some resin uses, or molecular weights and melting points as high as desired.

From a commercial standpoint, it is essential that a polyester resin be produced in the shortest possible time and the desired degree of polymerization be obtained. A polyethylene terephthalate resin suitable for melt spinning should have a carboxyl content value of about or below 50 equivalents per million grams (eq./ 10 gr. or meq./kg.), a melting point of preferably at least about 258260 C., and an intrinsic viscosity preferably not less than about 0.60 (determined in a phenol and 40% tetrachloroethane solution, 'wt./wt., at 30 C.), in order for the filaments formed therefrom to possess a satisfactory level of hydrolytic stability, thermal stability, ultra-violet light stability and a high degree of tenacity which is necessary for use of such filaments in the manufacture of fibers such as are used in wash and wear clothmg.

It is an object of the present invention to prepare highly polymeric linear polyesters by a direct esterification reaction between a dicarboxylic acid and a diol or by a transesterification reaction between an ester of a dicarboxylic acid and a diol, so as to form a polyester prepolymer and the polycondensation of the said polyester prepolymer in the presence of an improved polycondensation catalyst.

It is another object of the present invention to prepare a highly polymeric linear polyester resin by polycondensing bis-Z-hydroxyethyl terephthalate in the presence of an improved polycondensation catalyst.

These and other objects are accomplished in accordance with the present invention which involves a method for preparing highly polymeric linear polyesters wherein dimethyl terephthalate is reacted with ethylene glycol in the presence of an ester-interchange catalyst to form a polyester prepolymer or where terephthalic acid is reacted with ethylene glycol in the presence of a first stage catalytic additive to form a polyester prepolymer and where the resulting polyester prepolymer is polycondensed in the presence of a polycondensation catalyst, the improvement comprising carrying out the polycondensation of the polyester prepolymer in the presence of a catalytic amount of a suitable metal salt of hydrofluoric acid.

The metal salts of hydrofluoric acid or metal fluorides that are used as polycondensation catalysts in the present method may be suitably varied to meet any requirements of reaction conditions and desired product. While the present invention is not to be limited to any particular suitable metal fluorides, it has been found that the preferred metal fluorides are those wherein the metal component is from Groups IV-A, VII-B, and VIII of the Periodic Table (see Merck Index, 6th ed., inside front cover). For example, among the polycondensation catalysts that can be used in accordance with the present invention are lead fluoride, cobaltic fluoride, manganous fluoride, and manganic fluoride, or any combination thereof.

The preparation of polyesters via the ester-interchange reaction is generally carried out with a molar ratio of glycol, such as ethylene glycol, to a dialkyl terephthalate, such as dimethyl terephthalate, of from about 1:1 to about 15:1, respectively, but preferably from about 1.221 to about 2.6:1. The transesterification reaction is generally carried out at atmospheric pressure in an inert atmosphere such as nitrogen, initially at a temperature range of from about 125 C. to about 250 C., but preferably between about 150 C. and 200 C. in the presence of a transesterification catalyst. During the first stage of this reaction, methyl alcohol is evolved and is continuously removed by distillation. After a reaction period of about 1 to 2 hours, the temperature of the reaction mixture is raised to from about 200 C. to about 300 C. for approximately one to three hours in order to complete the reaction, so as to form the desired polyester prepolymer and distill off any excess glycol.

Any known suitable transesterification or ester-interchange catalyst, for example, lithium hydride or zinc acetate, can be used to catalyze the present transesterification reaction. Generally, the transesterification catalyst is used in concentrations of from about 0.01% to about 0.20%, based on the weight of the dialkyl terephthalate used in the initial reaction mixture.

Similarly, the preparation of polyester resins via the direct esterification reaction is generally carried out with a molar ratio of glycol, such as ethylene glycol, to a dicarboxylic acid, such as terephthalic acid, of from about 1:1 to about 15:1, but preferably from about 1.2:1 to about 26:1. The direct esterification step is generally carried out at temperatures ranging from about 180 C. to about 280 C. in the absence of an oxygen containing atmosphere at atmospheric or elevated pressure for about two to four hours to form the desired polyester prepolymer. For example, the reaction may be carried out in an atmosphere of nitrogen.

Any known suitable first stage direct esterification catalytic additive may be used in the direct esterification step of the present method. For example, calcium acetate and triethyl amine may be used. The first stage catalytic additives are generally used in concentrations ranging from 5X10 mole to about 5X10 mole of catalytic additive per mole of terephthalic acid present in the initial terephthalic acid-glycol reaction mixture.

The polycondensation step of the present invention is accomplished by adding a suitable metal salt of hydrofluoric acid to a polyester prepolymer or bis-Z-hydroxyethyl terephthalate and heating the blend thereof under reduced pressure within the range of from about 0.05 mm. to .20 mm. of mercury while being agitated at a temperature of from about 260 C. to about 325 C. for from two to four hours. In accordance with the present invention a metal salt of hydrofluoric acid is generally employed in amounts ranging from about 0.01% to about 0.2% based on the weight of the polyester prepolymer to be polycondensed. Usually, it has been found that from about 0.02% to about 0.1% of the subject polycondensation catalyst is preferred in most instances. Higher or lower concentrations of metal fluondes can also be used in the subject poly-condensation reaction. However, when concentrations less than the above are used, its effectiveness is generally reduced, whereas if concentrations greater than this are used, no further improvement in the present method or desired product is generally obtained.

The following examples of several preferred embodiments of the present invention will further serve to illustrate the present invention. All parts are by weight unless otherwise indicated.

EXAMPLE I A mixture comprising 600 g. of dimethyl terephthalate, 396 mls. of ethylene glycol, and 0.24 g. of lithium hydride was charged into a reaction vessel equipped with a nitrogen inlet, heating means and stirring means. The reaction mixture was agitated and heated at atmospheric pressure at 198 C. under a nitrogen blanket. The reac tion mixture was held at about 198 C. for about two hours, during which time lay-product methyl alcohol was distilled off. Then the temperature of the reaction mixture was allowed to rise to 230 C. over a period of about one hour to distill off any remaining by-product methyl alcohol and ethylene glycol and form a polyester prepolymer. The prepolymer product was allowed to cool under an atmosphere of nitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of lead fluoride (PbF and placed in a reaction vessel. The reaction mix was heated to about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of. the polyester prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.66, a carboxyl content value of 9.3 (meq./kg.) and a melting point of about 266 C.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of cobaltic fluoride (CoF and placed in a reaction vessel. The reaction mix was heated to about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the polyester prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.69, a carboxyl content value of 13.5 (meq./kg.) and a melting point of about 263 C.

EXAMPLE IV Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of cadmium fluoride (CDF and placed in a reaction vessel. The reaction mix was heated to about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the polyester prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.69, a carboxyl content value of 12.0 (meq./ kg.) and a melting point of 257 C.

EXAMPLE V Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of thallous fluoride (TlF) and placed in a reaction vessel. The reaction mix was heated to about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the polyester prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.64, a carboxyl content value of 7.4 (meq./kg.) and a melting point of about 258 C.

EXAMPLE VI A blended mixture comprising 474 g. of terephthalic acid, 288 mls. of ethylene glycol and 149 mls. of triethylamine was charged into a reaction vessel equipped with a nitrogen inlet, a Dean-Starke separating apparatus, heating means, and stirring means. The reaction mixture was agitated and the temperature was raised to about 197 C. under a nitrogen blanket at atmospheric pressure. At about C., a water-triethylamine azeotropic mixture started to distill off. The azeotropic mixture was continuously separated by means of the Dean-Starke apparatus, and the triethylamine recovered was continuously returned to the reaction vessel. The reaction mixture became almost clear. Then, the temperature was allowed to rise to about 220 C. over a one hour period to form a polyester prepolymer. The prepolymer product was allowed to cool under an atmosphere of nitrogen.

EXAMPLE VII Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of manganic fluoride (MnF and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.65, a carboxyl content value of 17.2 (meq./ kg.) and a melting point of about 262 C.

EXAMPLE VIII Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of manganous fluoride (MnF and placed in a reaction vessel. The reaction mixture was heated to about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.69, a carboxyl content value of 17.4 (meq./ kg.) and a melting point of about 261 C.

EXAMPLE IX Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of cobaltic fluoride (CoF )and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the prepolymer and formation of a poly ester resin. The polyester resin formed had an intrinsic viscosity of 0.75, a carboxyl content value of 26.3 (meq./

.kg.) and a melting point of about 264 C.

EXAMPLE X Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of cadmium fluoride (CdF2) and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the preploymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.73, a carboxyl content value of 24.7 (meq./ kg), and a melting point of about 261 C.

EXAMPLE XI Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of thallous fluoride (TlF) and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.72, a carboxyl content value of 13.7 (meq./ kg), and a melting point of about 262 C.

EXAMPLE XII Fifty grams of the prepolymer product of Example VI was mixed with 0.02 g. of lead fluoride (PbB and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under reduced pressure of from about 0.05 to about 0.1 mm. of mercury while under agitation for about three hours to bring about the polycondensation of the prepolymer and formation of a polyester resin. The polyester resin formed had an intrinsic viscosity of 0.74, a carboxyl content value of 15.9 (meq./kg.) and a melting point of about 265 C.

The intrinsic viscosity of the polyester resin products of the above examples were measured in a pheno and 40% tetrachloroethane solution (Wt/wt.) at 30 C.

The process of the present invention has been describe with particular reference to polyethylene terephthalate but it will be obvious that the subject invention include within its scope other polymeric polymethylene tereph thalates formed from glycols of the series HO (CH OH where n is 2 to 10 and terephthalic acid or esters thereo and copolyesters containing varied amounts of other suit able dicarboxylic acids or esters thereof, such as isophthalir acid.

The results in the above examples indicate that th presence of suitable metal fluorides during the polycon densation of the prepolymers of the direct esterificatiol or transesterification method of preparing polyethylem terephthalate accelerates the rate of polycondensation ant enhances the resulting polyester. The polyester resin: produced by the present method have high molecula: Weights, as indicated by their intrinsic viscosity, suitably high melting points, and low carboxyl contents, thereb] making such resins particularly suitable for melt spin ning into useful filaments.

It will be apparent that various different embodiment of this invention can be made practicing this inventioi without departing from the spirit and scope thereof, ant therefore, it is not intended to be limited except as in dicated in the appended claims.

We claim:

1. In a process of preparing highly polymeric linea polyethylene terephthalate resin wherein dimethyl tereph thalate is reacted with ethylene glycol in the presence 0 an ester-interchange catalyst to form a polyester pre polymer or Where terephthalic acid is reacted with ethyl ene glycol in the presence of a first stage catalytic additivr to form a polyester prepolymer and where the resulting polyester prepolymer is polycondensed in the presence 0: a polycondensation catalyst, the improvement comprising adding to said prepolymer a catalytic amount of a meta salt of hydrofluoric acid polycondensation catalyst where in the metal component of said salt is from Groups VII-B or VIII of the Periodic Table (Merck Index, 6th ed.) an( then carrying out said polycondensation reaction.

2. The process of claim 1 wherein the metal salt i present in an amount of from about 0.01% to abou 0.2%, based on the weight of polyester prepolymer.

3. The process of claim 1 wherein the metal salt i cobaltic fluoride.

4. The process of claim 1 wherein the metal salt i; manganous fluoride.

5. The process of claim 1 wherein the metal salt i manganic fluoride.

References Cited UNITED STATES PATENTS 3,220,982 11/1965 Advani 260-7. 3,057,824 10/1962 Le Bras et al. 2607f 3,254,055 5/1966 Smith 260-7. 3,345,337 10/1967 Koller et al. 260-71 FOREIGN PATENTS 6,402,214 9/ 1964 Netherlands.

247,005 5/ 1966 Austria. 1,053,133 12/1966 Great Britain. 1,297,516 5/ 1962 France.

WILLIAM H. SHORT, Primary Examiner L. P. QUAST, Assistant Examiner 

